It's from a high frequency coil in a switch mode power circuit on your mainboard, the sound is resonance from a coil. An easy way to fix this is to find the coil, and coat it with RTV silicone.
Link to wikis on the sound it makes.
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Physics? Ha! This is clearly magic and devilry at work. Prepare firewood! We have witches to burn!
Senior Engineering Technician (AEET).